I could say that CNC routing is a subtractive process of manufacturing while 3D is additive. In CNC routing, unwanted material is cut e.g. when making a curve. 3D printing on the other had adds material on something. layers of material are laid upon each other in order to arrive at the desired shape.

I tend to think that the other difference is that Spinning drill bits are used in CNC routing to carve plastics, metal and wood while 3D printing mostly use computers in controlling print heads that deposit layers of other materials such as plastic in 3D dimensions